Cadmium-free quantum dots as time-gated bioimaging probes in highly-autofluorescent human breast cancer cells

Abstract

We report cadmium-free, biocompatible (Zn)CuInS(2) quantum dots with long fluorescence lifetimes as superior bioimaging probes using time-gated detection to suppress cell autofluorescence and improve the signal : background ratio by an order of magnitude. These results will be important for developing non-toxic fluorescence imaging probes for ultrasensitive biomedical diagnostics.

Figure 1

Absorption and photoluminescence spectra of CIS/ZnS and CdSe/ZnS QDs

Figure 2

Lifetime decay curves of CdSe/ZnS QDs, CIS/ZnS QDs and SK-BR-3 cells with and without CIS QDs. Average Lifetime is calculated from multi-exponential fitting: τ_avg = Σ_i A_iτ_i, with i = 3, A_i is the fractional amplitude (Σ_i A_i = 1) and τ_i are the lifetimes of each decay component

Figure 3

Fluorescence intensity images with two cells labeled 1 and 2 that are difficult to quantify in terms of extent of labeling; Middle row: FLIM images; ranging from 1ns (blue) to 16 ns (red); Bottom row: Image after time-gating the first 10 ns of photons significantly improving contrast, and removes unlabeled cells from the images.

Figure 4

Fluorescence intensity images and cross-sections in x and y to compare the signal (s): background (b) levels of CIS/ZnS-labeled cells as a function of the time-gate applied.